VISUAL RECOGNITION OF SPATIAL FREQUENCY INFORMATION IN DIAGNOSTIC INTRAORAL ROENTGENOGRAMS

• Published in: Shika Hoshasen Vol. 28; no. 3; pp. 267 - 284
• Main Author: TSUCHIYA, Toshio
• Format: Journal Article
• Language: Japanese
• Published: Japanese Society for Oral and Maxillofacial Radiology 1988
• ISSN: 0389-9705; 2185-6311
• DOI: 10.11242/dentalradiology1960.28.267

The purpose of this study was to determine the ideal spatial frequency band for use in intraoral roentgenographical diagnosis. It is postulated that the results of this study may provide a positive indication of film resolving power using enhanced film speeds for intraoral roentgenography. The experimantal procedure was as follows: After fixation of the focus-object distance, the object-film distance was kept away. By modifying the object-film distance, varied frequency band reduction images could be obtained. Band reduction images obtained in this manner were duplicated to dental size. Based on these roentgenograms, experienced dentists evaluated whether the periodontal space and laminadura were determinable [Yes] or not [No] in diagnosis. Eleven dentists, each having over five years of clinical experience, participated in this study. Frequency bands having in the object—film distances for which a positive [Yes] answer was obtained from one half of these dentists, and for which a negative [No] answer was obtained from the remaining dentists were regarded as the frequency bands required for diagnosis. The film used was Ektaspeed ready pack E-2 film (KODAK Co.) for roentgenography and X-Omat duplicating film (KODAK Co.) for the duplicating procedure. Four areas of the jaw, including the dried incisor and molar regions of the upper jaw, and the incisor and molar regions of the lower jaw were used as representative for this study. The scattering material used was water phantom (4cm). The results obtained can be summarized as below: 1. The cut-off spatial frequency when the periodontal space and laminadura were examined and diagnosed, using roentogenograms obtained from intraoral roentogenographic system, was 6.2lp/mm for the upper incisor region, 4.5lp/mm for the upper molar region, 4.8lp/mm for the lower incisor region and 5.8lp/mm for the lower molar region. The necessary diagnostic information was obtained when the spatial frequency band ranged between 7.0 and 8.0lp/mm in the intraoral roentgenography. 2. It was established that scatter originating from the soft tissue of the jaw decreased image contrast which further negatively affected the diagnostic recognition of spatial frequency. 3. Using the bisecting angle technique, the spatial frequency band mentioned above was obtainable with an angle of tooth axis and film of less than 40°.